What does Isaiah 57:6 mean?

You’ve chosen your idols among the smooth stones in the riverbeds. You pour out drink offerings and bring grain to them. Should I be happy about this? Isaiah 57:6 - Modern Text Bible

(God points out that the people are worshiping idols, using stones from riverbeds as objects of devotion, and offering sacrifices to them. He’s making it clear that this is not something He approves of.)